In the combustion of a fuel, such as coal, oil, peat, waste, etc., in a combustion plant, such as those associated with boiler systems for providing steam to a power plant, a hot process gas (or flue gas) is generated. Such a flue gas will often contain, among other things, carbon dioxide (CO2) The negative environmental effects of releasing carbon dioxide to the atmosphere have been widely recognised, and have resulted in the development of processes adapted for removing carbon dioxide from the hot process gas generated in the combustion of the above mentioned fuels. One such system and process has previously been disclosed and is directed to a single-stage Chilled Ammonia based system and method for removal of carbon dioxide (CO2) from a post-combustion flue gas stream.
Known solvent based CO2 capture systems, such as ammonia based systems and processes (CAP) provide a relatively low cost means for capturing/removing CO2 from a gas stream, such as, for example, a post combustion flue gas stream. An example of such a system and process has previously been disclosed in pending patent application PCT/US2005/012794 (international Publication Number: WO 2006/022885/Inventor: Eli Gal)), filed on 12 Apr. 2005 and titled Ultra Cleaning of Combustion Gas Including the Removal of CO2. In this process the absorption of CO2 from a flue gas stream is achieved by contacting a chilled ammonia ionic ammonia solution (or slurry) with a flue gas stream that contains CO2.
FIG. 1A is a diagram generally depicting a flue gas processing system 15 for use in removing various pollutants from a flue gas stream FG emitted by the combustion chamber of a boiler system 26 used in a steam generator system of, for example, a power generation plant. This system includes a CO2 removal system 70 that is configured to remove CO2 from the flue gas stream FG before emitting the cleaned flue gas stream to an exhaust stack 90 (or alternatively additional processing). It is also configured to output CO2 removed from the flue gas stream FG. Details of CO2 removal system 70 are generally depicted in FIG. 1B.
With reference to FIG. 1B, CO2 removal System 70 includes a capture system 72 for capturing/removing CO2 from a flue gas stream FG and a regeneration system 74 for regenerating ionic ammonia solution used to remove CO2 from the flue gas stream FG. Details of capture system 72 are generally depicted in FIG. 1C.
With reference to FIG. 1C and FIG. 1D, a capture system 72 of a CO2 capture system 70 (FIG. 1A) is generally depicted. In this system, the capture system 72 is a solvent based CO2 capture system. More particularly, in this example, the solvent used is chilled ammonia. In a chilled ammonia (CAP) based system/method for CO2 removal, an absorber vessel is provided in which an absorbent ionic ammonia solution (ionic ammonia solution) is contacted with a flue gas stream (FG) containing CO2. The ionic ammonia solution is typically aqueous and may be composed of, for example, water and ammonium ions, bicarbonate ions, carbonate ions, and/or carbamate ions. An example of a known CAP CO2 removal system is generally depicted in the diagrams of FIG. 1C and FIG. 1D.
With reference to FIG. 1C, an absorber vessel 170 is configured to receive a flue gas stream (FG) originating from, for example, the combustion chamber of a fossil fuel fired boiler 26 (see FIG. 1A). It is also configured to receive a lean ionic ammonia solution supply from regeneration system 74 (see FIG. 1B). The lean ionic ammonia solution is introduced into the vessel 170 via a liquid distribution system 122 while the flue gas stream FG is also received by the absorber vessel 170 via flue gas inlet 76.
The ionic ammonia solution is put into contact with the flue gas stream via a gas-liquid contacting device (hereinafter, mass transfer device, MTD) 111 used for contacting the flue gas stream with solvent and located in the absorber vessel 170 and within the path that the flue gas stream travels from its entrance via inlet 76 to the vessel exit 77. The gas-liquid contacting device 111 may be, for example, one or more commonly known structured or random packing materials, or a combination thereof.
Once contacted with the flue gas stream, the ionic ammonia solution acts to absorb CO2 from the flue gas stream, thus making the ionic ammonia solution “rich” with CO2 (rich solution). The rich ionic ammonia solution continues to flow downward through the mass transfer device and is then collected in the bottom 78 of the absorber vessel 170. The rich ionic ammonia solution is then regenerated via regenerator system 74 (see FIG. 1B) to release the CO2 absorbed by the ionic ammonia solution from the flue gas stream. The CO2 released from the ionic ammonia solution may then be output to storage or other predetermined uses/purposes. Once the CO2 is released from the ionic ammonia solution, the ionic ammonia solution is said to be “lean”. The lean ionic ammonia solution is then again ready to absorb CO2 from a flue gas stream and may be directed back to the liquid distribution system 121 whereby it is again introduced into the absorber vessel 170. Details of regenerating system 74 are shown in FIG. 1E. System 74 includes a regenerator vessel 195. Regenerator vessel 195 is configured to receive a rich solution feed from the capture system 72 and to return a lean solution feed to the capture system 72 once CO2 has been separated from the rich solution.
During the regeneration process, the rich ionic ammonia solution is heated so that CO2 contained in the solution separates from the chilled ammonia solution. Once separated from the CO2, ammonia (ammonia slip) is returned to the capture system for use in capturing further CO2 from a gas stream.
These currently known solvent based CO2 capture technologies typically consume approximately 20-30% of the power generated by the power generation system in order for the CO2 capture process to work effectively. In addition, these technologies often require a large portion of thermal energy generated by boiler/re-boiler functions (reboiler duty) in order to regenerate amine solution for re-use in capturing CO2 from a flue gas stream. In short, while there are known technologies for capturing CO2 from a flue gas stream, they require immense amounts of energy in order to function well. Further, in order to maximize/optimize the amount of time that flue gas is in contact with amine, the physical size of the absorber and/or re-generator tanks in a typical system must be very large. The cost to design and implement these towers of such large scale is very high. Additionally, the physical space that is required on-site to accommodate these vessels is significant. Where on-site space is limited, additional steps must be taken to implement the vessels/system in the limited space, if possible.